Field of the Invention
Embodiments of the present invention relate to an organic light emitting display device.
Discussion of the Related Art
Various flat panel displays such as liquid crystal display device, plasma display panel and organic light emitting display device are now used. The organic light emitting display device has attracted attention because it has a rapid response speed and a low power consumption. In addition, because the organic light emitting display device emits light itself, there is not a problem related with a viewing angle.
In more detail, FIG. 1 is a circuit diagram illustrating a pixel structure of related art organic light emitting display device. Referring to FIG. 1, each pixel includes a switching transistor (Tsw), a driving transistor (Tdr), a capacitor (Cst), and an organic light emitting diode (OLED). Further, the switching transistor (Tsw) is switched by a scan pulse (SP) supplied to a scan control line (SL), and the switching transistor (Tsw) supplies a data voltage (Vdata) supplied to a data line (DL) to a driving transistor (Tdr).
In addition, the driving transistor (Tdr) is switched by the data voltage (Vdata) supplied from the switching transistor (Tsw), and the driving transistor (Tdr) controls a data current (bled) flowing to the OLED from a driving power source (EVdd) supplied from a driving power line. As shown, the capacitor (Cst) is connected between gate and source terminals of the driving transistor (Tdr), where the capacitor (Cst) stores a voltage corresponding to the data voltage (Vdata) supplied to the gate terminal of the driving transistor (Tdr), and turns-on the driving transistor (Tdr) using the stored voltage.
The OLED is electrically connected between cathode line (EVss) and source terminal of the driving transistor (Tdr), whereby the OLED emits light by the data current (Ioled) supplied from the driving transistor (Tdr). Further, each pixel (P) controls an intensity of the data current (Ioled) flowing in the OLED by switching the driving transistor (Tdr) according to the data voltage (Vdata), whereby the OLED emits light, thereby displaying a predetermined image.
However, in the related art OLED, the threshold voltage (Vth) characteristics of the driving transistor (Tdr) may be different in each position due to non-uniformity when manufacturing the thin film transistor. Accordingly, even though the data voltage (Vdata) is identically applied to the driving transistor (Tdr) for each pixel, a uniform picture quality is difficult to achieve because of the deviation of the current flowing in the OLED.
In order to overcome the problem related to the non-uniformity of picture quality, the Unexamined Publication Number P10-2012-0076215 in the Korean Intellectual Property Office discloses an OLED including a sensor transistor for each pixel, which enables external compensation techniques for sensing a threshold voltage of driving transistor through a reference line connected with the sensor transistor, and compensating for the threshold voltage of driving transistor. However, the number of reference lines is the same as the number of pixel columns so that it is difficult to design a source driver (D-IC) due to the increased number of channels of source driver (D-IC).